Histopathology of enucleated intraocular melanomas irradiated with cobalt and ruthenium plaques.

Eight malignant uveal melanomas irradiated with Stallard's 60Co applicator or Lommatzsch's 106Ru/106Rh applicator were studied by light microscopy and immunohistochemistry to analyse tumour cell morphology, antigenic expression and inflammatory cell infiltration in relation to radiation dose. The tumours were enucleated 1 to 24 months after irradiation because they did not regress or continued to grow. One patient has later died of metastatic disease. Eight uveal melanomas that were not irradiated were studied for comparative purposes. Radiation necrosis was found only in two cases. In four irradiated and in one control melanoma conspicuous collagen fibres were present in the basal part of the tumour. No difference was noted between the two groups in the number of mitotic figures or in the morphology of tumour cells. In all cases but one, more than half of the tumour cells were variably positive for S-100 protein. Neuron-specific enolase-positive melanoma cells were few in number and occurred in small clusters, and were somewhat more common in irradiated cases. A few lymphocytes and macrophages, which were preferentially found near the choroid, infiltrated every melanoma, but only single cells were associated with radiation necrosis. A mild scleritis near the tumour was present irrespective of irradiation. Although the melanomas were quite large for irradiation, the lack of necrosis in optimally irradiated basal parts of the tumour additionally indicates substantial radioresistance.